VFD/Motor Taking down CANOPN network
VFD/Motor Taking down CANOPN network
(OP)
We have 3 Square D VFD's (10, 15, and 40 HP) on a CANOPN network connected to a PLC. Whenever we start the 10 or 15 HP motors, our CANOPN network drops out. The drives begin to start up then fail. The 50 HP VFD/motor does not exhibit this behavior.
If we disconnect the leads from the VFD to the motor and then start the VFD, the network continues to operate. This is the case for either the 10 or 15 HP motor.
If we disconnect the CANOPN cable that connects the drive to the network, then start the VFD in HAND with motor connected, the CANOPN network drops out.
We've considered everything from line reactors to shielded motor cabling. The problem is that the 50 HP unit does not exhibit this behavior. All 3 VFD's are in the same enclosure. The motors are within 15 feet from the VFD's.
The hidden clue is that the CANOPN network still drops out even if the network cable is detached from the VFD. Any help would be much appreciated.
KCRider
If we disconnect the leads from the VFD to the motor and then start the VFD, the network continues to operate. This is the case for either the 10 or 15 HP motor.
If we disconnect the CANOPN cable that connects the drive to the network, then start the VFD in HAND with motor connected, the CANOPN network drops out.
We've considered everything from line reactors to shielded motor cabling. The problem is that the 50 HP unit does not exhibit this behavior. All 3 VFD's are in the same enclosure. The motors are within 15 feet from the VFD's.
The hidden clue is that the CANOPN network still drops out even if the network cable is detached from the VFD. Any help would be much appreciated.
KCRider





RE: VFD/Motor Taking down CANOPN network
The size of the drive has very little with the level of emitted EMI to do. So draw no conclusion from the fact that the 50 HP drive gives no problems.
This kind of problem is so common that most of us have to deal with them at least once each month.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD/Motor Taking down CANOPN network
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If we learn from our mistakes I'm getting a great education!
RE: VFD/Motor Taking down CANOPN network
That said, its only likely to present an issue if you only see the problem when more than one drive is running.
In terms of trying to fix the problem, Gunnar is right. The only thing I can think of that would get close is a scope and a current clamp to see just what noise is floating around. Of course, the scope by itself won't solve the problem.
A former employer had an issue with overcurrent on a particular conductor, it melted the insulation on a few units before the problem was finally identified. Turns out the current at the carrier frequency was about 4 times the 50Hz fundamental, and it wasn't that apparent until the scope came out.
RE: VFD/Motor Taking down CANOPN network
Neil
RE: VFD/Motor Taking down CANOPN network
No use to speculate. Get someone with the right equipment and experience to sort it out for you.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD/Motor Taking down CANOPN network
I agree with Gunnar that this is a very typical RFI (Radio Frequency Interference) issue.
High Frequency noise will be polluting the serial communication signal and the likely issue will be the installation and probably ineffective bonding of the motor, VFD and any other connection you have in the vicinity of the VFD.
By the sound of it, the bonding is not working too well and the 'noise' is going into the serial comms connection and affecting your canbus waveform.
Put a scope on your canbus signal and look at the noise on the signal.
The VFD acts like a major emitter of HF noise, they all do. The trick is to ensure the majority of this HF noise goes to ground through low impedance conductors; braid, flat straps, 360deg termination of the shield, metal gland nuts on the motor if the screen is terminated in the motor gland, segregation of power cables from control cables, and so on. The VFD manual you have will/should explain all this.
Do not start spending money on expensive RFI filters (yet). Get your installation right first or you will be wasting your money.
I'm guessing you are in the US with your use of HP and the "SqD".
The laws and regulations on EMC (ElectroMagnetic Compatibility) are not as stringent as in Europe and Australia but the problems are the same..
RE: VFD/Motor Taking down CANOPN network
Disconnecting the CAN-bus from the smaller VFD's had NO EFFECT on the network dropping out. In other words, the network continues to drop when the drives are energized even with the CAN-bus cable disconnected! - more support for the RFI theory.
We'll be taking more readings on Monday, and I'll report back on what we found.
Thanks again.
KCRider